On Fri, Nov 22, 2019 at 11:31 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > > > I was also considering setting xino=on by default if xino_auto > > > > is enabled, because what have we got to loose? > > > > > > > > The inodes whose st_ino fit in lower bits (by far more common) will > > > > use overlay st_dev and the inodes whose st_ino overflow the lower bits > > > > will use pseudo_dev. Seems like a win-win situation, but I wanted to > > > > get your feedback on this before sending out a patch. > > > > > > > > > > Arrr.. yes, there is a catch. > > > Overflowing lower bits has a price beyond just using pseudo_dev. > > > It introduces the possibility of inode number conflicts on directories, > > > because directories never use pseudo_dev. > > > > > > > But we could mitigate that problem if we reserve an fsid for volatile > > directory inode numbers. get_next_ino is 32bit anyway. > > I am going to take a swing at having xino=auto always enabling xino. > > > > FWIW, pushed WIP branch to: > https://github.com/amir73il/linux/commits/ovl-ino > > It is based on an updated ovl-layers branch of the $SUBJECT series. > > During cleanup, I've found several corner cases bugs of setting > i_ino value and fixed them. > None of those bugs are critical. > AFAIK, the only user that complained on inconsistent i_ino is > an xfstest that is checking ino in /proc/locks. > > However, I do think that the cleanup I made simplifies the code > which was a bit spaghetti in that area and with some more TLC > we can get to enabling xino from xino=auto even for filesystems > that have seldom high ino bits. > > That could be a real benefit, because it is unlikely that users > will have enough knowledge or certainty about underlying fs > to declare xino=on. > > I need to clear up some time to test i_ino changes and > the collision avoidance code, but for now, at least the ovl-ino branch > passes the existing regression tests. > Documenting all this in words has become too complex for me, so I resorted to visual aids [1]. The table doesn't mention this explicitly, but xino=auto can now (code in ovl-ino) provide all desired features for any non-samefs setup. Tests are still WIP. Will post the work when they are done. I am using a nested overlay [2] as a way to test xino overflow behavior. Thanks, Amir. [1] https://github.com/amir73il/linux/blob/ovl-ino/Documentation/filesystems/overlayfs.rst#inode-properties [2] https://github.com/amir73il/unionmount-testsuite/commits/ovl-nested
